Snapshot Generator

Creates Snapshot infrastructure for optimizing event sourcing aggregate rebuilds.

When to Use

Component Characteristics

Snapshot

• Immutable state capture of an aggregate at a point in time
• Properties: aggregateId, aggregateType, version, state (JSON), createdAt
• Supports

  fromArray()

  /

  toArray()

  for serialization
• Version must be >= 1

SnapshotStoreInterface

• save(Snapshot $snapshot): void

  — persist snapshot (upsert)

• load(string $aggregateId): ?Snapshot

  — retrieve latest snapshot

• delete(string $aggregateId): void

  — remove all snapshots for aggregate

SnapshotStrategy

• Configurable event threshold (default: 100)

• shouldTakeSnapshot(int $eventsSinceLastSnapshot): bool

• Determines when a new snapshot should be captured

AggregateSnapshotter

• Application service coordinating snapshot operations
• Loads aggregate from snapshot + remaining events
• Takes snapshots when strategy threshold is met

Generation Process

Step 1: Generate Domain Components

Path:

src/Domain/{BC}/Snapshot/

1. Snapshot.php

   — Immutable snapshot value object

2. SnapshotStoreInterface.php

   — Repository interface for snapshot persistence

Step 2: Generate Application Components

Path:

src/Application/{BC}/Snapshot/

1. SnapshotStrategy.php

   — Configurable threshold strategy

2. AggregateSnapshotter.php

   — Application service for snapshot operations

Step 3: Generate Infrastructure Components

Path:

src/Infrastructure/{BC}/Snapshot/

1. DoctrineSnapshotStore.php

   — Doctrine DBAL implementation of SnapshotStoreInterface
2. Database migration SQL for snapshots table

Step 4: Generate Tests

1. SnapshotTest.php

   — Construction, serialization, validation tests

2. SnapshotStrategyTest.php

   — Threshold behavior tests

3. AggregateSnapshotterTest.php

   — Load and take snapshot tests

File Placement

src/Domain/{BC}/Snapshot/

src/Application/{BC}/Snapshot/

src/Infrastructure/{BC}/Snapshot/

tests/Unit/Domain/{BC}/Snapshot/

tests/Unit/Application/{BC}/Snapshot/

Naming Conventions

Snapshot

Snapshot

SnapshotStoreInterface

SnapshotStoreInterface

SnapshotStrategy

SnapshotStrategy

AggregateSnapshotter

AggregateSnapshotter

DoctrineSnapshotStore

DoctrineSnapshotStore

{ClassName}Test

SnapshotTest

Quick Template Reference

Snapshot

final readonly class Snapshot
{
    public function __construct(
        public string $aggregateId,
        public string $aggregateType,
        public int $version,
        public string $state,
        public \DateTimeImmutable $createdAt
    ) {
        // version >= 1 validation
    }

    public static function fromArray(array $data): self;
    public function toArray(): array;
}

SnapshotStoreInterface

interface SnapshotStoreInterface
{
    public function save(Snapshot $snapshot): void;
    public function load(string $aggregateId): ?Snapshot;
    public function delete(string $aggregateId): void;
}

SnapshotStrategy

final readonly class SnapshotStrategy
{
    public function __construct(
        private int $eventThreshold = 100
    ) {}

    public function shouldTakeSnapshot(int $eventsSinceLastSnapshot): bool;
}

Usage Example

$snapshotter = new AggregateSnapshotter($snapshotStore, $strategy);

// Load aggregate from snapshot + remaining events
$result = $snapshotter->loadWithSnapshot($aggregateId, $eventStore);
$snapshot = $result['snapshot'];
$remainingEvents = $result['remainingEvents'];

$aggregate = $snapshot !== null
    ? Order::fromSnapshot($snapshot)
    : new Order($aggregateId);

foreach ($remainingEvents as $event) {
    $aggregate->apply($event);
}

// Take snapshot if threshold reached
$snapshotter->takeSnapshotIfNeeded(
    aggregateId: $aggregateId,
    aggregateType: 'Order',
    version: $aggregate->getVersion(),
    state: $aggregate->toSnapshot(),
    eventsSinceSnapshot: count($remainingEvents)
);

Database Schema

CREATE TABLE snapshots (
    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
    aggregate_id VARCHAR(36) NOT NULL,
    aggregate_type VARCHAR(255) NOT NULL,
    version INT UNSIGNED NOT NULL,
    state JSON NOT NULL,
    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
    UNIQUE INDEX idx_snapshots_aggregate_id (aggregate_id),
    INDEX idx_snapshots_aggregate_type (aggregate_type)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

Anti-patterns to Avoid

References

For complete PHP templates and examples, see:

• references/templates.md

  — Snapshot, SnapshotStoreInterface, SnapshotStrategy, AggregateSnapshotter, DoctrineSnapshotStore templates

• references/examples.md

  — OrderAggregate integration, event sourcing examples and tests